Rated 5 out of 5 stars

Priceless!

Very useful for inter-language communications.

It's a bit limited, since it doesn't support retaining the prefix added by the client (because the addon runs when the composing window is presented, which includes the prefix already). In order to work this around, use a negative lookahead:

(?!^)(Ref|Tr|Re|Fwd):\s+